Vapor generating, superheating, and reheating method and apparatus therefor



2 Sheets-Sheet 1 C. R. CHAN |NvEN-roR Charles/E Chaz? BY TToRNl-:Y

METHOD AND APPARATUS THEREFOR /r I 1||l||l||l78 VAPOR GENERATING. SUPERHEATING, AND REHEATING May 12, 1959 Filed Aug. 23, 1951 May 12, 1959 A C, R CHAN 2,886,013

VAPOR GENERATING, SUPERHEATING, AND REHEATING METHOD AND APPARATUS THEREFOR v Filed Aug. 23. 1951 2 Sheets-Sheet 2 OOOOOOOOOOUOIOQOOO'DOO O 0 00000000000005000000 00000000 www eaoaaoo 00 006 noy 'no G a Q la a on on D 00 00 o woon Q 0500000 90000000 www nonna INVENTOR Char/6,51?. @izan N TTORNEY United States Patent O VAPOR GENERATING, SUPERHEATING, AND REHEATING METHOD AND APPARATUS THEREFOR Charles R. Chan, Pompton Lakes, NJ., assignor to The Babcock & Wilcox Company, Rockleigh, NJ., a corporation of New Jersey Application August 23, 1951, Serial No. 243,267

4 Claims. (Cl. 122-478) This invention relates to vapor lgenerating and superheating apparatus, and more particularly, to an improved construction and method of operation of a high capacity steam generator including a substantial amount of convection heated steam superheating and steam reheating surface. To attain the desired high capacity in such a unit the heating requirements necessitate a plurality of fuel burners spaced across the width of the installation. Such a burner arrangement may result in undesirable gas temperature variations at positions transversely of the furnace, and particularly at low operating loads when only a fraction of the total number of burners are in use. Again, in some installations, the fired burners distributed across the width of the installation operate with different combustion efficiencies so that an unbalance of heat liberation transversely of the furnace results.

This invention involves a convection steam heating section having a symmetrical arrangement of convection heated reheater and superheater surface in three parallel gas passes and associated gas ilow control means at the outlet sides of the gas passes for regulating the portions of the heating gases directed over the superheater and reheater surfaces respectively. The arrangement also pre mits regulation of the heating gas flow so that the heat absorbed remains Within safe tube metal temperature limits irrespective of the gas temperature leaving the furnace.

The invention more specifically involves a high capacity steam generating unit having a furnace of the radiant type in which almost all of the steam generating surface is located, a convection superheater, a convection reheater, a recirculated gas system for raising steam superheat and reheat temperatures over a load range below a predetermined control point, gas by-pass means, for regulating steam superheat and reheat temperatures over a load range above the predetermined control point, and a damper system for proportioning heating .gas ilow between the superheater and reheater over the entire con* trol range.

The invention will be described with reference to an embodiment thereof which is shown in the accompanying drawings and other objects of the invention will appear as the description proceeds.

In the drawings:

Fig. 1 is a sectional elevation of a high pressure steam generator, taken on the line 1-1 of Fig. 2, illustrating the invention; and

Fig. 2 is a plan section on the line 2--2 of Fig. l.

ers 40. The latter are shown as disposed outside of the front wall 12 of the furnace and protected thereby from contact with the furnace gases. The downcomers are disposed in an auxiliary chamber 42 (Fig. 2) formed in part by the furnace wall 12 and the auxiliary wall 44.

On the same side of the furnace as the downcomers are a plurality of superposed rows of fuel burners 46- 48, herein illustrated as pulverized fuel burners. There are three burners 46 in the top horizontal row, three burners 47 in the intermediate row, and three burners 48 in the lower horizontal row. Representative posip tions of the burners across the installation are indicated The vapor generating installation shown in the drawings includes a furnace 10 having front and rear walls 12 and 14 including upright vapor generating tubes 16 and 18 respectively. The furnace also includes side walls 20 and 22 (Fig. 2) having vapor Vgenerating wall tubes 24 and 26 respectively. A11 of the wall tubes having their upper ends in communication with the steam and water drum 30, and their lower ends connected to suitable headers 32--36 which in turn are connected to the liquid space of the drum by appropriate downcomby the center lines A-A, B--B, and C--C in Fig. 2. The burners are served by three pulverizers with valved connections from each pulverizer for supplying pulverized fuel and primary air to one row of burners, so that cutting out one pulverizer would cut out the corresponding row of burners. The number of burners utilized at any one time is dependent upon boiler load and the load may be so low that only two burners are needed. In that event only one pulverizer would be operated to supply the two burners with fuel and air. There would obviously be an unbalanced generation of heating gases across the width of the installation, under this condition, or with less than all of the burners in operation.

Some of the rear wall generating tubes 1S have oppositely inclined sections 50 and 52 extending along the upper and lower walls 54 and 56 of an arch construction 58 which extends into the furnace from the plane of the rear wall 14. These tubes have upper sections 62 extending in spaced relationship across the gas flow path from a secondary superheater 64 to the inlets 66 and 68 respectively of a gas by-pass 70 and three side-by-side gas passes 72-74 at the rear thereof. Tube sections 76 connect the tube sections 62 to the drum 30 and delineate the roof 78 of the furnace. Other rear wall tubes extend along the lower surface of the arch and have vertical sections 80 extending across the gas outlet of the furnace in front of the secondary superheater 64 and thence in alignment with the roof tubes 76 to the drums 30. The remaining rear wall tubes 1S extend vertically in staggered relation to the tube sections '62 and thence to the drum 30.

In the convection section rearwardly of the secondary superheater 64, the by-pass 70 contains vertically spaced economizer sections 82--84 disposed between an auxiliary wall 86 in vertical alignment with the furnace rear wall 14, and a rear wall 88 (Fig. 2) which includes upright saturated steam conducting tubes 90 which lead to a U-shaped superheater inlet header 92 of a primary superheater from a distributing header 94. The upright portions of the tubes 90 are spaced apart and the intervening spaces are lled with refractory material 96 rup to a position near the top of the primary superheater section 98. Above this level, the spaces between tube sections 90 are open to provide for gas flow into the space 68 above the passes 72-74.

The primary superheater has two similar parts. One of these parts is located in the gas pass 72, as shown in Fig. 2, and the other part is located in gas pass 74. These gas passes are symmetrical with reference to the intermediate reheater gas pass 73. Each superheater part is constructed as indicated in Fig. l. It consists of a plurality of superheater sections 98'-102. These sections are formed by series connected return bend tubes for the flow of steam from the superheater header 92 to two similar intermediate superheater headers 93. Steam temperature indicating devices 99 are associated with the headers 93 of the two primary superheaters.

Steam is supplied to the lower superheater header 92 through the tubes 90 and the tubes 110 and 114 leading from the saturated steam distributing header 94 and Patented May 12, 1959 also through side wall tubes 129 from side wall headers 132 to the side wall legs 130 of the header 92. Header 94 receives steam directly from the steam space of the drum 30 by appropriate tubular connections 113. The upright superheater supply tubes 110 extend along the rear wall 108 of the gas pass from the header 112 to which the tubes 114 are connected. These tubes 114 support the roof 116 above the convection passes and the by-pass 70.

Steam flows from the outlet headers 93 of the primary superheater through tubes 115, parts of which extend along the roof of the installation. The outlet ends of these tubes are directly connected to the single inlet header 122 of the secondary superheater 64.

Steam, after passing through the serially connected tubes of the secondary superheater 64 passes to an outlet 120, and thence through connections 118 to a point of use. Temperature indicators 119 are provided in the connections 118.

The primary superheater passes 72 and 74 are seprated from the gas pass 73 by vertical walls 104 and 106. Both the passes 72 and 74 and the central reheater pass are symmetrical to the center line of the unit. These walls extend from the wall 88 to the rear wall 108 and separate the passes throughout their length.

The gas outlet of each of the gas passes 72-74 has its own separately operable series of control dampers, or gas How regulators, such as 140. Adjacent these gas flow regulators there are other regulators 142 extending across the gas outlet of the by-pass 70. Gases flowing past the three series of gas ow regulators 140 or regulators 142 continue through the breeching or ductwork 150 to an air heater 152 and thence through ductwork 154 to a flue.

The convection heated reheater located in the middle pass 73 receives low pressure steam from the exhaust of a high pressure steam turbine through connections 151 to its inlet header 153. The reheater is of a multi-bank construction similar to that of the primary superheater section, having laterally spaced serially connected return bend. elements arranged similarly to 98-102 The upper ends of the elements are connected to the outlet header 155 from which a connection 157 delivers the reheated steam to the inlet end of the low pressure steam turbine. A temperatureV indicating device 159 is associated with the outlet connection 157.

For aiding in maintaining superheat temperatures at a predetermined value over lower portions of the desired load control range, a ilue gas recirculation system is provided including ductwork 160 leading from the breeching 150 to a gas recirculating fan 162, the outlet of which is so connected to the furnace hopper 164 by ductwork 166 that recirculated gases may be passed in controlled quantities upwardly throughout the full width of the hopper into the furnace. The flow of furnace gases is controlled by regulating the speed of the fan and/or by control of a damper 16S disposed in the ductwork 166. As the load decreases below a selected control point corresponding to the load at which the desired superheat and reheat temperatures will be obtained by the proportioning and arrangement of the heat transfer surface and without operation of the described regulating devices, increasing percentages of gas are recirculated to reduce furnace wall heat absorption and provide sutiicient heat to the convection steam heating surfaces to overcome their normal dropping steam temperature characteristics. For example, such gas recirculation may be increased as the load drops from the predetermined control point, such as 85% of peak load capacity, until 28% of the stack gases are recirculated at 60% of peak load.

For operation at loads above the selected control point, the superheat and reheat temperatures are maintained at the desiredvalues by operation of the dampers 140 and 142 to `reduce the vamount of heating gases owing through the passes -7274. As the .load increases, the gas by-pass is opened to by-pass increasing amounts of heating gases Cil 4 around the primary superheater sections andreheater to offset the normal tendency of the convection heated superheat and reheat temperatures to rise as the load increases. The temperature indicators 199 and 159 are used to determine the amount of damper operation for this control.

The control dampers for the primary superheater section passes 72 and 74 and reheater pass 73 are independently operated in response to the temperature indicators 199 and 159 to proportion the heating gas flow from the space 68 between these passes. This control supplements both the gas recirculation and by-pass controls and may be used in any part of the entire control range, i.e. from 60% of peak load to the peak load condition. inasmuch as the temperature curves of convection heated superheaters and reheaters will have different slopes due to the different steam conditions therein, this supplemental damper, control permits a proportioning of the gases at any load to offset such differences.

Whereas the invention has been described with reference to the specific embodiment shown in the drawings, it is to be appreciated that the invention is to be considered as not limited to all the details of the embodiment shown. For example, the arrangement of reheater and superheater surfaces in the gas passes 72-74 `may be such that the middle gas pass contains either a superheater or a reheater. If, as described herein, it contains a reheater, then the heating surface in the remaining passes is provided by superheater sections. Conversely, if all of the convection surfaces in the middle pass are provided by a convection superheater, then all of the surface of the remaining passes will be provided by a convection reheater.

I claim:

1. In a high capacity vapor generator; a furnace having a gas outlet; means firing the furnace; means forming a convection heat transfer zone for the ow of gases from the furnace; wall means dividing the convection heat transfer zone into at least threeparallel gas passes with two of the passes having the remaining pass arranged between them; the two outside passes being symmetrically arranged relative to the center of the gas outlet; a first convection heat absorbing unit including spaced reheater tubes; a second convection heat absorbing unit including spaced superheater tubes; one of said heat absorbing units being disposed in the middle pass and two like components of the remaining heat absorbing unit being disposed in the passes on opposite sides of the middle pass; wall means forming a gas by-pass means in parallel with said passes; the gas by-pass means extending across the generator with a part thereofalongside each of said parallel passes; gas flow control means operable to control the gas flow through the by-pass to maintain vapor temperature at a predetermined value at loads below a predetermined load; and a recirculated gas flow system including a fan and ductwork for recirculating furnace gases, at loads below said predetermined load, to the furnace from a position beyond at least a part of the vapor heating surface.

2. In a high pressure and high capacity vapor generating and superheating unit for power plants, a` large volume furnace having its walls and other boundaries including vapor generating tubes, means for firing the furnace at a position remote from the gas outlet of the furnace, a high temperature convection vapor heater including a bank of tubes disposed across all of the gas flow from the furnace outlet, the furnace being fired at a temperature above a safe value for contact with the superheater, the heat absorption of the furnace wall tubes intermediate the firing means and the superheater reducing they gas temperature to a safe value at the superheater outlet, wall means forming three paralleldownflow convection gas passes having gas inlets at their upper ends communicating withthe gas flow from the high temperature superheater, a. primary convection superheater and a convection reheater each having surfaces disposed in at least one of said downow gas passes, said downow gas passes being arranged in succession across the rear face of the unit and across the gas flow outlet of the high temperature superheater zone, wall means forming a downow gas bypass freely communicating with the gas downflow inlets of all of the downow gas passes and freely communicating at its upper end with the gas outlet of the high temperature superheater zone and disposed, in general, between the rear face of the furnace and the downilow passes, said gas bypass extending substantially over the Width of the unit and the Width of all of the downow gas passes, a recirculated gas flow system including a fan and associated ductwork with the gas inlet of the system communicating with gas flow from said downflow passes and having its outlet communicating with the furnace at a position remote from the position of the ring means and upstream therefrom in a gas flow sense, means for separately regulating the gas flow over any one of said downow gas passes independently of the ilow of gases through the bypass or any other of the downflow gas passes and independently of the recirculated gas ow through said system, means for independently controlling or regulating gas flow through said bypass, and means for controlling and regulating the gas flow from said recirculated gas flow system to maintain a predetermined superheat over a wide range of vapor generating load.

The combination o f claim 2 further characterized by the hopper bottom furnace red by pulverized fuel burners disposed in separate vertically spaced rows at positions substantially above the hopper bottom, and the outlet of the recirculated gas system being disposed in the zone of the throat of the hopper bottom.

4. The combination of claim 3 further characterized by the disposition of economizer surfaces within the gas bypass.

References Cited in the le of this patent UNITED STATES PATENTS 1,747,011 Kerr Feb. 11, 1930 1,789,401 Dary Ian. 20, 1931 1,872,138 Grady Aug. 16, 1932 1,959,100 Gordon May 15, 1934 2,109,840 Gordon Mar. 1, 1938 2,229,643 De Baufre Jan. 28, 1941 2,268,776 Pourchot Jan. 6, 1942 2,281,580 Hobbs May 5, 1942 2,287,798 Hardgrove June 30, 1942 2,298,700 Junkins et al. Oct. 13, 1942 2,330,240 Raynor Sept. 28, 1943 2,628,598 Van Brunt Feb, 17, 1953 FOREIGN PATENTS 504,114 Great Britain Apr. 14, 1939 473,744 Great Britain Oct. 19, 1937 523,810 Gear Britain July 24. 194.0 

